[code-reflection] RFR: Enhance OpWriter [v2]

[Paul Sandoz]

> Enhance OpWriter to support the following options
> 1. Drop an operation's descendants. This allows for writing just the operation "header".
> 2. Write an operation's result even if it is void. This allows for improved debugging and presentation in some cases, esp. when we refer to values uniformly (an operation whose result is void still has a value, just one that is not used.)
> 
> Also, consolidate the write operations, and remove the explicit insertion of a live feed at the end of writing an operation.

Paul Sandoz has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains five additional commits since the last revision:

 - Merge branch 'code-reflection' into op-writer-options
 - Further simplify
 - Merge remote-tracking branch 'upstream/code-reflection' into op-writer-options
 - Simplify.
 - Update writer.

-------------

Changes:
  - all: https://git.openjdk.org/babylon/pull/79/files
  - new: https://git.openjdk.org/babylon/pull/79/files/004e820d..99071aad

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=babylon&pr=79&range=01
 - incr: https://webrevs.openjdk.org/?repo=babylon&pr=79&range=00-01

  Stats: 436 lines in 6 files changed: 358 ins; 2 del; 76 mod
  Patch: https://git.openjdk.org/babylon/pull/79.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/79/head:pull/79

PR: https://git.openjdk.org/babylon/pull/79